Reclaiming waste products in the manufacture of sulfite fiber.



H. K. MOORE & B; WOLF.

REGLAIMING WASTE PRODUCTS IN T115 MANUFACTURE OF SULFIITE 'FIBEK.

APPLIUATION FILED BBQ 30, 1913.

1,110,454 Patelited Sept. 15, 1914.

VACUUM PUMP I I STORAGE TANK IQ STEAM 3 7 es 26 menfonsr Y m g/W 0 e o i QWZZOWZeg CS' UNITED STATES nTENT OFFICE. 2

HUGE K. MOORE AND ROBERT B. WOLF, OF BERLIN, NEW HAMPSHIRE.

RECLAIMING WASTE PRODUCTS IN THE MANUFACTURE OF SULFITE FIBER.

S'pecificatiou of Letters Patent.

Patented S pt- 5, 19145- Application filed December 30, 1913. Serial No. 809,525.

To all whom it may concern:

Be it known that we, HUGH K. Moons and ROBERT B. WOLF, citizens of the United States, and residents of Berlin, in the county of Coos and State of New Hampshire, have invented certain new and useful Improvements in Reclaiming Waste Prod.- ucts in the Manufacture of Sulfite Fiber, of which the-following is a specification.

This invention has relation to the reclamation of waste products in the manufacture of sulfite fiber, and more particularly to the recovery of the sulfur dioxid which, heretofore in actual practice, has escaped from the blow pit after the cooked charge has been delivered thereto from the digester.

In our previous application Serial No. 590,158, filed November 1, 1910, We have illustrated conventionally an apparatus'for and described a process of recovering sulfur dioxid by bringing the vaporsfrom the blow pit into contact with the chilled surfaces of a surface condenser, and condensing them, and then separating the sulfur dioxid from the other gases by absorption in a suitable absorber.

In order to revent the loss of sulfur dioxid, it is desirable that the products of condensation should be kept as near the boiling point as possible to prevent the absorption thereby of the sulfur dioxid. Further, to secure a greater strength of acid solution in the absorber, it is necessary to eliminate the presence of air in the apparatus during the blow. We accomplish these results by means which will be subsequently described herein.

On the drawing, in Figure 1 an apparatus is conventionally shown for carrying out our invention. Fig. 2 shows a section through the condenser.

The digester is illustrated at 1 and is of the type used in the manufacture of sulfite fiber; In it are placed the chips and the acid (calcium bisulfite and more or less free sulfurous acid), and, after the neck is sealed, steam is injected into the digester to bring the contents thereof to the pro .er tempera.- ture. If desired, sulfur dioxi may be injected into the digester in accordance w th our application Serial No, 541,246, filed February 1, 1910. After the wood has been cooked at the proper temperature for the proper length 0 time and the cellulose fibers have been freed from their cementing materials, the contents of the digester are blown in the usual way through the pipe 2 into a blow pit conventionally illustrated at;

3, which is constructed with the usual false bottom for permitting the escape of the waste liquors. As usual, the interior of the blow pit is at slightly less atmospheric pressure. Hence, when the contents of the digester of ordinary size are discharged into the blow pit at a steam pressure of say 45 to pounds per square inch (not including the pressure due to the static head), from 18,000 to 20,000 pounds of steam are liberated in the blow pit from the discharged water. The temperature of the contents of the digester varies from 250 F. to 320 F., and, as soon as the materials reach the blow pit, vapors arise therefrom and are conducted away through a vomit stack vapors, there has been an esca e of a certain amount of free sulfur d oxld which,

was not utilized in the cooking operation, The escape of this free sulfur dioxid is a serious menace to vegetation and is highly objectionable on account of the odor.

In accordance with our process, the vomit stack is closed to the atmosphere during the blow, and the vapors and gases are conducted to a surface condenser conventionally illustrated in Fig. 1 at 5. This surface con denser may be of any suitable or desired type. Preferably, as shown in Fig, 2, it is of the horizontal tfype and is provided with diaphragms 6, 6 orming compartments 7, 8 and 9, the'eompartments 7 and 8 commu nicating through tubes 10 passed throu h the chamber 9. Partitions 11 divide t e chambers 7 and 8 as shown, so that the cooling medium takes a sinuous path through the condenser. As shown in Fig. 1, the vomit stack discharges into the lower extension of compartment 9 through conduit 15, and the gases and vapors are caused to circulate upwardly and around the tubes. Cold water or any other suitable cooling medium is injected through the pipe 12 to the chamber 7, and passing through the tubes is discharged through the circulating pipe 13. The V9,- pors entering the condenser from the vomit stack are condensed and pass from the trap 16 througha pipe' 17 'to-a receptacle 18 from which they may be drawn by the valved discharge ipe 26. Ordinarily we employ water as tl 'ie cooling medium at its seasonable temperature, although in lieu thereof some other chilled cooling medium may be utilized, or thewater itself may be cooled prior -toits admission to the condenser.

The effect of condensation of the vapors is to reduce to liquid form the water vapor and such compounds as wood alcohol, benzaldehyde, acetone,-acetic acid, and other vapors which would condense at or slightly above" the temperature of the coolingmedium, the quantities, amounts and character of these compounds depending more or less upon the methods, temperature, etc.,'

used in cooking as well as the nature of the materials cooked. The application of the principle of recovering these compounds by condensing vapors arising from the blow pit, while herein described as applying to the sulfite process, may be applied to any other process in which free gases are dis- 1 charged.

The condensation of the water vapor to water permits the absorption by the condensed water ofonly a relatively small proportion of the free 'sulfur'dioxid gas which escapes with the vapor, and consequently the great portion of free sulfur dioxid which is uncondensed passes through the condenser and is conducted away therefrom by means of the pipel i to any absorbing apparatus, which is'illustrated as comprising a tower 19 "containing limestone. In the upper end of the tower is shown a sprinkler head 20 through which water is sprinkled into the tower. In the passage of the sulfur dioxid through the tower, it reacts with the lime and 'is finaly discharged" through the pipe 21-- as a solution of calcium bisulfite and free sulfurous acid. The effluent from'the tower 'is collected in a tank 22 from which it maybe drawn by a valved pipe 23. A vacuum pump 24 is connected to'the upper end of the tower. In -'the conduit leading to the vacuum pump, L-ha-ve indicated a regulator check valve .2e of- -any suitable cont u ti n, which will-open-when the vacuum *Kt case may be-ma be neutralized with lime' This has the e-fiect of precipitating the sul is'too great to avoid damage to the blow The product of nitration, which is 051.

lected -1n the tank 14E or -the tank 18' as the fur dioxid in the form' of calcium inonos'ul fid' (CasO which is removed by "passing'the materials through a filter ipress,

tr al. The filtrate contains acetic acid in the separated and removed by any well known leaving the filtrate practically clear and new,

process, such as evaporation, fractional distillation and precipitation by various reagents. The contents of the tank 22 may be used in the digesters in cooking the wood. The vomit stack 4 at a suitable point. has a luted cover 26v ar tially balanced by a weight 27 so that t e stack may be opened to the atmosphere. Immediately prior 'to the blow, steam is injected into the pit 3 through i a valved steam pipe 28 for the purpose of completely filling the. pit and Ethe stack with steam and thereby forcing therefrom any air which is contained therein. Then the cover or cap26 is closed, the supply of steam through the pipe 28 is cut off, the vacuum pump 24 is started, and then the contents of the digester are discharged into the blow pit. The steam in the blow pit, prior to the admission ofthe contents of the digester, rapidly condenses and there is substantially ,uo pressure above atmospheric pressure in the blow pit. The rising vapors ass from the vomit stack through the con uit 15 into'the condenser 5 and ar condensed as explained. The present invention provides for completely reclaiming the sulfur dioxid which has heretofore been lost in the operation of blowing the digesters into the blow pits. In addition to reclaiming the sulfur dioxid so that it may be again utilized, the present invention provides for reclaiming and utiliz- ;ing various other valuable products, such as methyl alcohol, benzaldehyde, acetone, acetic-acid and other organic acids and compounds.

We have stated that a small proportion of sulfur dioxid is absorbed by the water of condensation in the condenser. Preferably, therefore, the water of condensation-is maintained at a temperature but slightly less' than the boiling pointso as to limit the absorption thereby of the free sulfur dioxidp' But utilizing the horizontal surface con densing the vapors from theblow pit, the only water which can absorb the sulfur 'dioxid is that which has been condensed from the steam coming from the blow pit, and the water being brought out nearthe boiling point, it contains a minimum amount eater volume of,

of gas.- Consequently-the lOO vfree gas will not be absor ed by 'thewater.

but will pass on to the "absorbing tank or tower. Furthermore, by'the employment of a surface condenser, thev water, which used as the cooling medium and whichi i's' delivered from the condenser, isin aclean' heated condition and may be utilized for a variety of purposes for which it could not .be used ifit had been previously employed in the direct condensation of the vapors by contact therewith, because, in the latter case,

it would have absorbed a portion of the sul- :fu'r di xid t and other products from the blow p1 I =With lime to reclaim the sulfur dioxid absorbed therein. On the other hand, however, we may first subject the product of condensation to a vacuum for the purpose of liberating the sulfur dioxid which may be condensed or absorbed-in any suitable manner. The remaining product of condensation, which contains acetic acid, may be brought into the presence of metallic lead for the purpose of producing lead acetate, after which the remaining products may be recovered as previously indicated.

We have herein stated that, prior to the blow, the pit and vomit stack are swept clean of air by the injection of steam. This is a feature of great advantage as it relieves the vacuum pumps of the necessity of exhaust'ing the air from the pit and stack, and makes it possible to use a smaller vacuum pump than would otherwise be necessary on account of the presence of inert gases. Further, by eliminating the inert gases, a smaller absorption apparatus may be used. Because of the absence of air, a commercial or usable acid may be made in the absorption apparatus, since the effects of partial pressures are obviated. Furthermore, owing to the absence of air, an acid solutlon is obtained in which the portion of free sulfurous acid is greatly increased, and, in addition, there is no oxidation of the sulfur dioxid to trioxid.

What we claim is:

1. The herein described process of recovering sulfur dioxid, which consists in removing the air from a blow pit, discharging the contents of a digester into said blow pit, separating and recovering the pulp, condensing by surface condensation the vapors arising from said blow pit, and recovering the sulfur dioxid.

2. The herein described process of recovering sulfur dioxid, which consists in filling a blow pit with steam to remove the air therefrom, discharging the contents of a pulp'digester into the steam-filled blow pit, condensing by surface condensation the vapors arising from the blow pit, and thereby.

separating them from the sulfur dioxid, and recovering the sulfur dioxid.

3. The herein described process of recovering sulfur dioxid, which consists in first filling an open blow pit with steam to remove the air therefrom, then' closing the pit and connecting the same with an air pump, then discharging the contents of a pulp digester into said pit, and condensing the vapors rising from the blow pit, and recovering the uncondensed sulfur dioxid.

4. The combination with a digester and a blow pit, of a vomit stack leadin from the blow pit and having a remova le cap, a condenser connected to the vomit stack, and means for filling the blow pit with steam.

In testimony whereof we have affixed our signatures in presence of two witnesses.

HUGH K. MOORE. 7 ROBERT B. WOLF. 

